386 THE PROTOZOA 



in clusters, and according to Koch they fuse in pairs (Fig. 162, D 0} ; 

 cytological details of the syngamy, if such it be, are lacking (but compare 

 Theileria, infra). 



2. The stellate stage is succeeded by a spherical stage, very possibly repre- 

 senting the zygote. This body grows in size, but its development, as de- 

 scribed by Koch, is difficult to understand, and requires further elucidation. 

 The final result is a globular mass with a single nucleus, found in great numbers 

 on the third day, according to Koch (Fig. 162, J). Whether these bodies have 

 arisen by division of the zygote, or represent simply the zygotes, is not clear, 

 but the latter alternative seems the more probable. 



3. The globular stage is succeeded by a club-like or retort-shaped stage. 

 According to Christophers, whose account of the life-cycle appears to begin 

 at this stage, a split appears in the globular body, whereby a portion contain- 

 ing the nucleus is divided off incompletely from a portion which has no 

 nucleus. Tho non-nucleated portion then swings round and forms the tail- 

 piece of the complete club-shaped body, which has a single nucleus at the 

 swollen extremity. The club-shaped bodies appear to represent the ookinetes 

 (Fig. 162, K M). They are motile and gregarine-like, and in some cases 

 have an organ resembling an epimerite, regarded by Christophers as a boring 

 organ, at the anterior extremity. Their size is about four times that of the 

 piroplaswns in the blood. 



4. The club-shaped bodies pass from the gut of the tick into the ovary 

 and oviduct, and penetrate into the ova. There they become again globular 

 in form, and are found in the yolk of the egg, and later in the cells of the 

 embryo developed from the egg. When, however, the parasites have been 

 taken up by a nymph, as may happen in P. canis, the globular bodies are 

 found in the tissue-cells of the body. This globular stage, termed " zygote " 

 by Christophers, very probably corresponds to the oocyst of the hsemamcebae. 



5. The globular body of the previous stage divides up by multiple fission 

 into a number of " sporoblasts," which do not remain aggregated together, 

 but scatter themselves through the tissues of the tick, larva, nymph, or adult, 

 as the case may be. 



6. The sporoblasts divide in their turn into a great number of sporozoites, 

 small bodies with a single nucleus similar in appearance to the piroplasms in 

 the blood. The sporozoites collect in vast numbers in the salivary glands 

 of the tick, and pass into the vertebrate when next the tick feeds. According 

 to Gonder, ticks infected with Theileria parva purge their salivary glands com- 

 pletely of the parasites when they feed, and are only infective for a single meal. 



The development of Theileria parva in the tick has been described by 

 Gonder (740). Within an hour after passing into the stomach of the tick 

 the parasites become free from the corpuscles. The immature gametocytes 

 die off, but the adult forms proceed to gamete -formation. The free parasites 

 are at first rounded off, but soon send out processes and become amoeboid. 

 The male gametocytes send out a single process, and creep about actively 

 like a limax-amosbz ; their nucleus goes through an unequal division, after 

 which the gametocyte becomes a gamete. The female gametes, which are 

 inactive, go through a similar reduction- process. Pairing of two gametes 

 and fusion of the cytoplasmic bodies takes place, but before the nuclei fuse 

 each nucleus goes through a second reduction-division. After copulation of 

 the nuclei the zygote becomes an active ookinete, first retort-shaped and then 

 gregariiiiform, which penetrates into the salivary glands, and there goes 

 through a multiplicative process, very similar to that of Halteridium in the 

 lung of the pigeon (cf. Fig. 157), producing a swarm of sporozoites which are 

 inocuated into the vertebrate host by the tick. Thus in Theileria also 

 there is no flagellated stage at any part of the life-cycle a fact which does 

 not, however, prevent Gonder from seeing " blepharoplasts," and even crith- 

 idial forms on every possible occasion ; he seems to consider nuclear reduction 

 and blepharoplast -formation as the same thing. It is a pity that the effect 

 of such excellent work should be marred by so much theoretical bias. Aber 

 tvie die Alien sungen . . . ! 



